Methods of making a lignocellulose product and products resulting therefrom



fiber is lost.

United States atent METHODS OF MAKING A LIGNOCELLULOSE PRODUCT AND PRODUCTS RESULTING THEREFROM William T. Glab, Dubuque, Iowa, assignor, by mesne assignments, to Durel Incorporated, Dubuque, Iowa, a corporation of Iowa No Drawing. Filed Oct. 6, 1958, Ser. No. 765,335 2 Claims. (Cl. 106-163) This invention relates to methods of making a lignocellulose product and to the products resulting therefrom.

This application is a continuation in-part of my cop'ending application, Serial No. 443,711, filed July 15, 1954, now US. Patent No. 2,864,715.

It is an object of this invention to provide an improved method of making a moldable composition comprising reacting in the presence of steam an essentially dry mixture including comminuted lignocellulose and a material including lignin while confining the mixture of lignocellulose and reactant under superatmospheric pressure, preferably at about SOD-550 F. for a time that is preferably about 4-60 minutes.

Another object of the. invention is to provide an improved method of making a molded composition comprising reacting in the presence of steam an essentially dry mixture including comminuted lignocellulose and a material including lignin while confining the mixture under superatmospheric pressure, finely dividing the resulting product and molding at an elevated temperature and pressure.

A further object of the invention is to provide lignocellulose products prepared by the above methods.

Other objects and advantages of the invention will be apparent from the following description of several embodiments of the invention.

An important advantage of the invention appears to be the controlling of the reaction in the high pressure system so that the alpha cellulose is reduced in molecular size sutficiently to prevent swelling of subsequently fabri' cated products but not to the extent that toughness of This latter occurs under drastic degradation and starts to become quiteserious when approximately 25% of the lignocellulose has been lost as either gaseous or soluble by-products. Another advantage appears to be the controlling of the cellulose degradation to plasticize the lignin component so that it can subsequently be made to flow and function as a binder between the comminuted lignocellulose particles.

Another advantage is the provision of a relatively dry systemso that high capacity for the processing of, for example, wood wasteis attained. This is not possible in a wet process such as ordinarily found in a pulping process in which the reactor is" charged with approximately 90% Water which takes up space as well as requires the addition of large amounts of energy'to bring the reaction medium to the proper temperature.

Another advantage is the contacting of lignocellulose or dry mixes of lignocellulose and other ingredients under superatmospheric pressure with a vapor including steam or combination of vapors functioning both as a heat transfer medium and as a reactant.

A further advantage is the production of an extrudable composition wherein thereaction products may be extraded under a pressure of 2,000-20,000 pounds per square inch and in a temperature'range of 100-400 F to produce shaped articles.

Patented Jan. 17, lhi'il' In the method of this invention an essentially dry mixture including cornminuted lignocellulose and a material including lignin is heated together while confining the lignocellulose and the material under superatmospheric pressure as in an autoclave.

It appears that the hemicelluloses are the primary constituents of the lignocellulose which are attacked by hydrolysis, but that under the high pressure and temperature of this invention a portion of the hydrolysates are further converted to higher molecular weight materials which can function as plasticizers for the autoclave product when it is molded. At the same time a controlled degradation of the alpha cellulose is carried out to the extent that the desired degree of moisture stability is obtained in the molded or extruded products Without an unnecessary loss of toughness. These actions are believed to occur although they have not been absolutely ously in a continuous contactor.

The lignocellulose which appears dry to the touch actually contains up to about 30% water before the reaction begins.

The lignocellulose which may be used in this invention includes wood as well as other lignocellulosic vegetable materials. The lignocellulose is finely divided so that the particles are preferably not more than 20 mesh in size as measured by a standard screen although smaller sizes are preferred.

During the reaction which takes place in a confined atmosphere under superatmospheric pressure various reaction products are produced although the exact nature of the reactions is not understood. It appears that the reaction products are either inert so that the product itself is inert, have a binding action such as is true of the lignin produced, are gaseous by-products, or are polymerized. By hydrolyzing and partially removing, or polymerizing the hemi-celluloses to lignin type materials, the ratio of lignin and other binders to the alphacellulose is increased so that the general nature of the lignocellulose mixture is drastically ,changed.

The high pressure method of this invention has a number of advantages that are not possible with reactions taking place at ordinary pressures and in .an unconfined state. In the preferred process, steam is introduced into the autoclave both for heating purposes and to supply moisture for the reaction. In the high pressure method of this invention heat transfer is much more rapid so that in general a shorter reaction time is required. Furthermore, energy losses during the reaction are greatly reduced. In the ordinary reacting mixture these energy losses result from the release of volatile materials such as water vapor, gaseous reaction by-products and the like. As the reaction here takes place in a confined atmosphere, no such losses occur to any material degree. Furthermore, the energy supplied by the steam or vapor is utilized to heat only the lignocellulose with its approximately normal moisture content in contrast to pulping type reactions where large quantities of water are present, requiring far greater expenditures of energy.

Another important advantage of this process is the close control that is obtained over the reaction. Thus the temperature of the reacting mass, and hence the rate of reaction, can be easily raised or lowered by controlling the rate of flow, pressure and the temperature of the heat transfer medium which may be steam, oil vapor, or other high temperature fluids. Reactions may easily be stopped by flashing the heat transfer medium from the autoclave since the large energy loss on expansion cools the reacting mass below the incipient reaction point. During the practice of the process the reactingmixture may be confined in a jacketed vessel with the heating medium introduced to the chambers in the quantity and temperature desired.

A very important advantage of the invention is that volatile reactants may be used as the reacting mass is in a confined space. Volatile reactants are impossible, of course, when the reacting mass is in the open. As a result of the rapid heat transfer achieved by this invention and the penetration of volatile reactants the reaction not only proceeds to completion in a much shorter time but the final product tends to be more uniform than where the reactants are heated such as in an ordinary pI(1)C6SS that depends upon surface temperature differentia s.

Tests have shown that the confining of the reacting mass in the confined autoclave not only causes retention of the by-products of reaction within the mass even when the by-products are gaseous but also causes polymerization of all or a portion of these by-products, even some that are gaseous. in so-called wet processes large quantities of the by-products of reaction go into solution and are lost.

Another advantage of the invention is that the volatile by-products are easily collected and removed at low cost for later use where desired or to prevent the creation of a nuisance.

Where additional reactants and catalysts for the reaction are volatile no mechanical mixing of the ingredients is required. This results in a considerable saving in time, labor and other factors. Thus, in these instances, it is only necessary to charge the reactor with the lignocellulose and introduce the volatile materials including the ammonium hydroxide into the reactor under superatmospheric pressure. In addition, if desired, the reactants can be changed or modified during the course of a run. This is not possible to such a degree in a wet process where the charge generally contains less than 50% of lignocellulose, and addition of reactants would in many cases cause prohibitive amounts to go into solution.

A further advantage of utilizing a vapor process is that the volatile content of the reaction product which is primarily moisture can be controlled. By using superheated steam with a sufficient degree of superheat, products on the order of 1% or lower volatile content can be obtained. Under normal conditions, to degrees of superheat at 300 pounds per square inch steam pressure will produce a product of 3-5% volatile content. Thus the expensive drying step connected with wet processes can be avoided.

Because of rapid penetration of reactants under high pressure, larger sized particles can be charged to the autoclave than would ordinarily be used, and a savings in size reduction cost made as a result of lower power requirements to reduce the treated material in comparison with raw lignocellulose.

In addition, where fiat stock or preformed material is being made as in a sealed press, the products can be made much thicker and more uniform than in an ordinary press which depends upon high platen temperatures for heat transfer, and in many cases requires almost prohibitive cycle times.

The products of the reactions of this invention may be finished shaped materials or moldable compositions that may be used to make molded products. Where the product is molded after the reaction, this product is preferably removed from the reaction vessel and then ground to a fine powder that is preferably not over 50 mesh in size. The finely divided moldable material is heated to a temperature just sufiicient to cause the material to flow and fill the mold under the pressure used. This temperature is kept suificiently low, however, that losses are minor and breakdown due to decomposition is kept to a minimum. The preferred temperature is between 250400 F.

The molding pressure may be any pressure sufficient to cause the material to fill completely the mold and willvary depending upon the shape of the mold, the nature of the moldable material and other factors. In the preferred process to produce high density materials this pressure is between 2,000l0,000 pounds per square inch. The molding time is only suificient to cause the moldable material to fill the mold and set, and again will vary depending upon the type of mold being used, the temperature, the nature of the moldable material and similar factors. In general, the molding time will vary between 0.2-15 minutes.

The flow of the moldable material of this invention is improved and a shorter time is required if a plasticizer is added. Thus, by adding 10% aniline to the finely divided moldable composition of this process the plasticity is increased. Similarly, the plasticity is improved by adding 10% furfural.

Plasticizers in general which have been found to be effective with the moldable materials include water; aromatic compounds containing a hydroxyl group such as aniline, phenol and cresol; alcohols such as benzyl, diethyleneglycol, glycerol, and furfuryl; nitrogen compounds such as formamide, urea, pyridine, and triethanolamine; and furfural.

The preferred plasticizers are Water, furfural, aniline and phenol and the quantity utilized may vary depending on the flow desired. The preferred quantity is between about 220%.

In particular, the choice of plasticizer will depend upon the end use or method of fabrication of the material. The reaction products themselves are of a slow thermosetting nature. Thus, if a plasticizer such as water which is incapable of thermoset is used, the material is essentially of a thermoplastic nature. This is also true of the preferred plasticizers as a group, however, when desired, thermoset compositions can be made by using furfural, aniline or phenol in conjunction with a catalyst and, if desired, other materials capable of copolynierization.

Materials which will function as catalysts include the oxides, hydroxides and carbonates of the alkali and alkaline earth metals. The preferred catalysts are the'oxides of zinc and magnesium.

Among the materials which may be used with the thermosetting plasticizers as copolymers are hexamethylene tetramine, dimethylolurea, paraformaldehyde and urea.

Depending upon the set time required, about 0.5-5 .0% of the catalyst and about 0.510.0% of the copolymer are used.

If desired, thermoset products can be obtained without the use of catalysts or copolymers merely by heat treating the fabricated products after they have been molded or extruded.

If desired, products of density ranging from 0.2-1.3 specific gravity may be produced in the high pressure reacting vessel itself Without requiring a subsequent molding operation as described above with high pressure molding. Here the finely divided lignocellulose and the lignin,

' and other materials where used, are mixed and the mixture cold pressed into the desired shape or compacted in a. sealed press. The compressed mixture is then heated in the press or other high pressure vessel for the required time at the required temperature and pressure. The material when removed from the reaction vessel will then be found to be quite hard and strong.

Steam is preferably supplied at 100-1000 pounds per square inch pressure and at a temperature of 400550 F. In the event that a sealed press is used, the normal moisture content of the wood as well as the reaction byproducts may be used to build up to a predetermined pressure which can be maintained constant by venting the excess vapors produced. This pressure is preferably be tween 100-600 pounds per square inch. Such a procedure eliminates the blow-ups encountered in treating wood in an ordinary hot press at high temperatures, as well as drastically reducing press time, and polymerizes a percentage of the gaseous and low molecular weight by-prodnets to resinous-like materials which function as binders for lignocellulose particles. If desired, a two step process may be used in which the first step includes the pressure treatment and the second step includes venting the vapors to atmospheric pressure followed by a 2-10 minute heat treatment period before removing the material from the press or the autoclave.

Where lignin is reacted under high pressure-temperature conditions with lignocellulose in the presence of steam in a high pressure vessel such as an autoclave, it is preferably very finely divided and thoroughly blended with the finely divided lignocellulose in a mixing device prior to reaction.

In general this reaction can be modified by the inclusion of an alkali such as sodium hydroxide, which appears to butter the reaction, or by an acid salt such as calcium chloride which increases the reaction rate. Thus a wide variety of reaction products with different characteristics can be produced.

If an alkali is used in conjunction with lignin, the products can be formed into boards in a hot press and will possess superior strength, while boards having exceptional moisture resistance can be produced from reaction products where an acidic salt is used.

The preferred quantity of lignin is between about 230% by weight of the lignocellulose. When alkalies are used the preferred quantity is between about 0.5 10.0% of the lignocellulose, while acid salts are preferably added in an amount between about 0.25-6.0% by Weight of the lignocellulose. If sulfur is used along with lignin it is preferably used in an amount equal to about 2.0-20.0% by weight of the lignocellulose.

When soluble alkalies and acid salts are used, they are preferably added to the lignocellulose in the form of an aqueous solution, and then thoroughly blended with the lignocellulose to insure a uniform dispersion of the alkali or salt. The preferred quantity of solution added is between 5.0-20.0% by weight of the lignocellulose. The solution concentration will, of course, depend upon the desired amount of salt or alkali to be added. The lignin is preferably blended with the lignocellulose prior to the addition of the solution.

EXAMPLE 1 -Finely divided lignocellulose, containing only its normal moisture content of approximately 6% was mixed with 5% by weight of finely divided lignin for one-half hour in a ball-mill. This composition was then placed in a heated autoclave, and steam was admitted until the pressure was 300 pounds per square inch gauge, and the temperature was approximately 440 F. The autoclave was held under these conditions for minutes, and then the steam was rapidly flashed ofi. During the course of the run, the pressure was maintained at 300 psi. by venting off the excess pressure caused by volatile reaction by-products. The granular reaction product which had been cooled below the incipient reaction point by the rapid steam flash-off was removed from the autoclave, and all particles which had consolidated were thoroughly broken up. The moisture or volatile content of this material was approximately 10%.

In the same manner as specified in Example 1 lignin was reacted with lignocellulose at superatmospheric pressure in the presence of steam in conjunction with a number of other materials. The following table sets forth the composition and the autoclave conditions under which these reaction products were made.

Table I Autoclave Percent Example Lignin Additive Time, Temp., Press., Min. F. p.s.i.

2 5.0 None 25 440 300 5.0 0.5% Sodium Hydroxide 25 440 300 5.0 1.0% Sodium Hydroxide. 25 440 300 5.0 -do 30 440 300 5.0 do 40 440 300 5.0 2.0% Sodium Hydroxide 25 440 300 10. 0 1.0% Sodium Hydroxide..- 25 440 300 5. 0 2.0% Calcium Chloride.-. 20 440 300 5.0 2.0% Magnesium Chloride. 15 440 300 5. 0 0.5% Ammonium Chloride. 20 440 300 5.0 2.0% Zinc Chloride I5 440 800 5. 0 1.0% Ferric Chloride 20 440 300 5.0 1.0% Aluminum Sulfate... 20 400 200 6.0 2.021 lgiammonium Phos- 25 440 300 p a e. 5. 0 20% Sulfur 215 440 300 15.0 12.0% Sulfur. 2'0 440 300 15. 0 5.0% Aniline 25 440 300 15.0 5.05% Anili e+2.0% Zinc 25 440 300 in e. 20 15.0 5.0% Pyridine 25 440 300 21 15.0 5.03; Ammonium Hydrox- 25 440 300 1 e. 22 5. 0 3.0% 'lar Base A 25 440 300 23 10.0 do 25 440 300 All of the percentages given in the above table are by weight of the lignocellulose. Where organic bases such as aniline, pyridine and tar bases are used they are preferably added in an amount equal to 0.5-15.0% by Weight of the lignocellulose.

Having described my invention as related to the embodiments set out herein, it is my intention that the invention be not limited by any of the details of description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

I claim:

1. The method of making a moldable and extrudable composition, consisting essentially of: intimately mixing finely-divided essentially dry lignocellulose with about 2-30% lignin by weight of the lignocellulose; and heating the resulting composition in the presence of steam at a temperature of about 300550 F. in a confined atmosphere at a gauge pressure of between about 100-1000 pounds per square inch for a time between about 4-60 minutes.

2. A moldable and extrudable method of claim 1.

product prepared by the References Cited in the file of this patent UNITED STATES PATENTS 2,692,206 Othmer et al Oct. 19, 1954 FOREIGN PATENTS 497,477 Great Britain Dec. 16, 1938 528,355 Canada July 31, 1956 

1. THE METHOD OF MAKING A MOLDABLE AND EXTRUDABLE COMPOSITION, CONSISTING ESSENTIALLY OF: INTIMATELY MIXING FINELY-DIVIDED ESSENTIALLY DRY LIGNOCELLULOSE WITH ABOUT 2-30% LIGNIN BY WEIGHT OF THE LIGNOCELLULOSE; AND HEATING THE RESULTING COMPOSITION IN THE PRESENCE OF STEAM AT A TEMPERATURE OF ABOUT 300-550*F. IN A CONFINED ATMOSPHERE AT A GAUGE PRESSURE OF BETWEEN ABOUT 100-1000 POUNDS PER SQUARE INCH FOR A TIME BETWEEN ABOUT 4-60 MINUTES. 